Self-clearing self-cutting implant

ABSTRACT

The invention relates to methods of stabilizing bone implants, including inserting a self-tapping implant having at least two helical grooves running in opposite directions around the implant.

RELATED APPLICATIONS

This is a divisional patent application which claims the benefit ofpriority from U.S. patent application Ser. No. 13/087,454 filed on Apr.15, 2011, which claims the benefit of priority from U.S. ProvisionalPatent Application No. 61/390,367 filed on Oct. 6, 2010 and U.S.Provisional Patent Application No. 61/147,630 filed on Jan. 27, 2009,and is a continuation-in-part of U.S. patent application Ser. No.12/694,055 filed on Jan. 26, 2010, which claims the benefit of priorityfrom U.S. Provisional Patent Application No. 61/147,630 filed on Jan.27, 2009.

FIELD OF INVENTION

The invention relates to bone implants, namely screw-type implants and,more particularly, to a self-tapping dental implant having at least twohelical grooves running in opposite directions around the implant.Implants of the present design are easier to insert and are less proneto micromotion than other known implants in the art.

BACKGROUND OF THE INVENTION

It has been discovered that micromotion, movement of an implant relativeto the bone it is implanted in, can induce bone absorption around theimplant and lead to failure. See Trisi, et al, Implant micromotion isrelated to peak insertion torque and bone density. Clin. Oral. Impl res,20 (2009) pp 467-71. This movement is believed to destroy the new cellsforming in the gap between the bone and implant. In which event, thetendency is for the bone to resorb around the implant to provide aperceived need for clearance. This leads to weakening and potentialfailure of the implant. To reduce failure, there is a need for animplant which has very high initial stability. To maximize success ofdental implants, the micromotion should not exceed 50-100 μm at theimplant/bone interface. Pillar, et al., Clin Orthop Relat Res. 1986July; (208):108-13.

Implants which are designed for a tight fit in the bone generallyrequire significantly more torque to insert.

Implants for insertion into living bone, including screw type implantsare widely used and are well known in the art. Such implants may be usedin dentistry or orthopedics. The screw tapping implants generally fallinto the category of self-tapping implants and non-self-tappingimplants. Non-self-tapping implants are merely threaded and are screwedinto the bone after it is separately drilled and tapped. Self-tappingimplants contain cutting threads analogous to those in a metal tap whichcut threads into the bone when inserted in a drilled hole that issmaller than the self-tapping implant diameter. The basic structure ofboth types of implants comprise a generally cylindrical main body thathas a set of external screw threads on the outer surface which engagewith threads cut into the bone. The engagement of the threads providesfor initial stabilization for the implant. With both types of implants,long term stability is provided by growth of new bone around theimplant. A non-self-tapping implant is usually tapered at the end whichis inserted into the bone. The other end of both implants contains ameans for attaching a dental prosthesis such as a tooth and is oftenthreaded to facilitate attachment of the prosthesis.

Self-tapping implants usually contain a more pronounced taper at the endof the implant on which the cutting threads of the tap portion of theimplant are disposed.

Self-tapping devices of the prior art suffer from a number of drawbacks.The thread cutting abilities of present devices are limited due to thethickness of the threads which creates large amounts of bone chips aspart of the cutting process. Current designs are unable to effectivelyclear these bone chips from the hole. Many devices contain flutes whichare substantially parallel to the body of the implant and adjacent tocutting surfaces to aid in clearing bone. The collection of chipsresults in an increase in the torque required to seat a self-tappingimplant. The increase in torque adds to patient discomfort and may alsolead to breakage of the threads cut in the bone. The inability of theimplant to clear debris can also prevent a surgeon from properly seatingan implant. The seating and insertion torque problems increase as thelength of the implant increases.

Self-tapping implants of the present invention are also ideally suitedfor osseointegrated hearing aids. Designs in the art suffer from slow orweak osseointegration. Movement of the implant further contributes toresorption of bone in the vicinity of the implant. Existing implantsalso get loose due to mechanical loading on the implant.

The art contains examples of implant designs having grooves within thecutting surfaces for removing debris.

Published United States patent application US20080187886A1 discloses aself-tapping dental implant having a vertical groove for collectingdebris.

Published United States patent application US20080160483A1 discloses aself-tapping implant having a vertical groove for collecting debris.

Published United States patent application US20080131840A1 discloses aself-tapping implant having a groove for holding debris.

Published United States patent application US20080081316A1 discloses aself-tapping implant having a vertical groove for containing debris.

Published United States patent application US20080038693A1 discloses aself-tapping implant having a vertical groove for containing debris.

U.S. Pat. No. 7,281,925 and published United States patent applicationUS20080032264A1 disclose a self-tapping implant having a groove cutwithin and parallel to the self-tapping threads for containing debris.

Published United States patent application US20080014556A1 discloses aself-tapping implant having a groove running with the threads forcontaining debris.

U.S. Pat. No. 7,273,373 discloses a self-tapping implant having a groovefor containing debris and protrusions to aid in anchoring.

Published United States patent application US20070190491A1 discloses aself-tapping implant which is out of round and has breaks in theself-tapping threads for passage of debris.

Published United States patent application US20070099153A1 discloses aself-tapping implant having a substantially vertical groove in theself-tapping threads for passage of debris.

Published United States patent application US20040121289A1 discloses aself-tapping implant having a substantially vertical groove running inan opposite direction to the cutting threads for passage of debris.

U.S. Pat. No. 6,604,945 discloses a self-tapping implant having asubstantially vertical groove running for passage of debris.

Published United States patent application US20020102518A1 discloses animplant having a vertical groove for passage of debris.

U.S. Pat. No. 6,273,722 discloses an implant with helices running inopposite directions. However, this is not a self-tapping implant.

U.S. Pat. No. 5,984,681 discloses a self-tapping implant having openthreads and a separate anchor.

U.S. Pat. No. 5,871,356 discloses an implant having vertical grooves forthe passage of debris.

U.S. Pat. No. 5,601,429 discloses an implant having grooves for clearingdebris running in the same direction as the cutting grooves.

U.S. Pat. No. 4,498,461 discloses an osseointegrated hearing aid.

U.S. Pat. No. 7,116,794 discloses an implant for anchoring a hearingaid.

It has been discovered that micromotion, movement of an implant relativeto the bone it is implanted in, can induce bone absorption around theimplant and lead to failure. See Trisi, et al, Implant micromotion isrelated to peak insertion torque and bone density. Clin. Oral. Impl res,20 (2009) pp 467-71. To reduce failure, there is a need for an implantwhich has very high initial stability. However, implants which aredesigned for a tight fit in the bone generally require significantlymore torque to insert. Despite the above examples, there is still a needin the art for a self-threading implant which is easy to install yetoffers acceptable holding power.

OBJECTIVE OF THE INVENTION

It is an objective of this invention to provide an improved self-tappingimplant having reduced torque for insertion and an increased loadbearing surface at the time of insertion.

It is an objective of the invention to provide an improved self-tappingimplant having reduced insertion torque and improved stability for usein anchoring dental devices to bone.

It is an objective of the invention to provide an improved self-tappingimplant having reduced insertion torque and improved stability for usein anchoring orthopedic devices to bone.

It is an objective of the invention to provide an improved self-tappingimplant having reduced insertion torque and improved stability for usein anchoring osseointegrated hearing aids to bone.

SUMMARY OF THE INVENTION

The present invention comprises a self-tapping implant which requiressubstantially less torque to install than a traditional self-tappingimplant having full screw threads. The reduction in effort is achievedby the inclusion of at least one cutting surface on each rotation of thethread and by including a spiral groove which runs in an oppositedirection to the threads. This enables the implant of the presentinvention to corkscrew into an opening instead of cutting coursethreads.

Implant designs of the present invention generate significantly lessbone debris that the “classic tap cutting grooves”. In the presentinvention, debris, are evenly distributed across the implant bodylength, rather than “collected” and compressed into either the groovesof the tap or the bottom of the hole in which the implant is beinginserted.

According to one embodiment the implant comprises a substantiallycylindrical body 1 having a proximal end 2 and a distal end 3. The bodycontains at least one external helical thread 9 which runs from thedistal end 3 to the proximal end 2. The helical thread 9 may be right orleft handed and contains at least one cutting edge 6 for each turn ofthe cutting head. The implant further comprises a second helix 10running in the opposite direction of the helical thread.

Implants of the present design can be used in dental, surgical, hearingaid applications or any application where a stable support is requiredin bone.

An unexpected benefit of the design of the present invention is thereduction of micromotion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a dental implant according to oneembodiment.

FIG. 2 is a distal end view of a dental implant according to oneembodiment.

FIG. 3 is an expanded side view of the implant in FIGS. 1 and 2.

FIG. 4 is a side view showing a secondary helix.

FIG. 5 is a side view showing the details for a particular embodiment ofa dental implant.

FIG. 6 is a graph of insertion torque for a dental implant according toone embodiment.

FIG. 7 is a graph of insertion torque for a dental implant using priorart designs.

FIG. 8 is a graph comparing the average insertion torque of the presentinvention to a prior art design.

FIG. 9 is a composite line graph comparing the insertion torque for animplant of the present invention with conventional fluted and non-flutedimplants

FIG. 10 is a composite line graph comparing the micromovement of animplant of the present invention with conventional fluted and non-flutedimplants.

FIG. 11 is a drawing illustrating an osseointegrated implant for ahearing aid.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a self-tapping implant which requiressubstantially less torque to install than devices currently in use, yethas significantly reduced micromotion immediately upon insertion. Thereduction in effort is achieved by the inclusion of at least one cuttingsurface on each rotation of the thread about the body of the implant andby including a spiral groove which runs in an opposite direction to thethreads. This enables the implant of the present invention to corkscrewinto an opening instead of cutting course threads as is done in the art.

Referring to FIGS. 1-3, according to one dental implant embodiment, theimplant comprises a substantially cylindrical body 1 having a proximalend 2 and a distal end 3. The proximal end contains a prostheticplatform 7 onto which a prosthesis will be fitted. The body contains atleast one external helical thread 9 which runs from the distal end 3 tothe proximal end 2. The helical thread 9 may be right or left handed andcontains at least one cutting edge 6 for each turn of the cutting head.The implant further comprises a second helix 10 running in the oppositedirection of the helical thread. The second helix 10 is cut atapproximately the same depth as the external helical thread 9. Thesecond helix can be seen more clearly in FIG. 4 in which the helicalthread 9 has been omitted for clarity.

The helical thread 9 is further comprised of an inner, or minor,diameter 11 and an outer, or major, diameter 12. The outer diameter 12forms a ridge 4 having a plateau 5 on the outermost thread surfaceswhich engages with the bone during insertion. It is preferred that theplateau 5 be as narrow as possible subject to the structural limitationsof the material comprising the implant. Thinner diameters allow forsmaller pilot holes, easier drilling and reduce the torque required forinsertion. Larger plateaus may be required for softer bone.

The thread pitch 15 is not critical to the invention and may beincreased or decreased depending on the mechanical needs for theapplication. Thread pitch can be constant or variable.

The helical thread 9 comprises a recess 13 and a beveled surface 14. Theangle of the bevel is not critical but should be as narrow as possibleto facilitate cutting into the bone, but not so narrow that thestructural integrity of the cutting surface and thread is comprised.

The cutting edge 6 is formed by cutting the second helix 10 into thebody of the implant and is contiguous with the helical thread 9. In apreferred embodiment, the thread 9 has a chamfer 30 adjacent the cuttingedge. The chamfer 30 makes contact with the bone following the cuttingedge 6. The second helix, 10 in addition to creating the cutting edge 6,also serves to assist in clearing bone debris created by the cuttingedge.

The main body 1 may be straight or tapered, with a straight body beingmost preferred. When the main body it is straight is preferred that theinitial turn of the helix 16 be of a smaller diameter than the rest ofthe main body 1 to facilitate easy insertion into the pilot hole.

In yet another embodiment a secondary thread (not shown) may be includedinside the helical thread 9.

FIG. 5 shows an embodiment in which the implant is 4 mm in length andhas an outer diameter 12 of 0.1540 cm and an inner diameter 11 of 0.12cm. The distance between the leading edges of the thread 9 is 0.354 cmand each thread has a 15° undercut on the bottom side and a cut having aradius of 0.015 cm on the top side. The secondary helix 10 is cut at adepth of 0.130 cm. The top of the secondary helix forms the cutting edge6 and is cut at a 60° angle which results in the cutting edge beingraked such that the leading edge is raked away from the direction of thethread 9.

One of skill in the art will appreciate that the surface of the implantcan be further processed to aid in growth of new bone around it. Suchprocessing can include the use of coatings or modifying the surfacetextures of the implant as is known in the art.

The prosthetic platform may be structured to accommodate any form ofimplant. It can comprise internal threads (not shown) which are insidethe body of the implant or external threads (not shown) or comprise anytype of stud or ball upon which a prosthesis can be mounted. The threadpitch is not critical and may be selected for the application. In yetother embodiments, the implant may contain surfaces suitable for bondingthe prosthesis to the implant.

The implant of the present invention is used in a conventional manner.The dentist or surgeon will drill a pilot hole for the implant. Theimplant is attached to an insertion tool and turned into the pilot hole.Upon turning, the cutting edge 6 will cut a groove into the bone intowhich the helical thread 9 will follow. Because cutting edge 6 has asharp edge leading into a narrow plateau on the helical thread 9, lessbone debris is generated. This debris is pushed towards the proximal endof the body through the second helical groove 10. This movement ofdebris keeps the pilot hole relatively free from debris therebypreventing debris from filling the pilot hole or binding or jamming theimplant. This reduces incidences of the implant prematurely bottomingout in the pilot hole because of debris filling the hole and reduces thedebris caught in the helical groove thereby reducing friction on thecutting surfaces which reduces the torque required for insertion.

Manufacturing

Implants of the present invention can be manufactured from anystructural material suitable for dental implants, including but notlimited to stainless steels, titanium, ceramics, polymers and any othermaterial with appropriate mechanical characteristics which isbiocompatible. Titanium is most preferred. Implants of the presentinvention can be readily manufactured using a modern lathe capable ofcutting screw threads. The unfinished stock is mounted in the lathe atthe proximal end. The cutting blade of the lathe cuts a helical groovein the stock leaving the desired primary thread. The direction ofrotation is then changed and the desired secondary helical groove is cutacross the primary thread thereby creating the cutting surfaces. Theshape of the helices is determined by the cutting head on the lathe anddifferent cutting heads can be used to create different helices. It willbe appreciated that both straight and tapered implants can be created inthis manner.

Alternatively, depending on the manufacturing materials, the implant canbe formed by passing the stock comprising the body through one or morecutting dies as is known in the art or by the use of molds or forging.For implants made of plastics, ceramics or polymers, molding is thepreferred method of manufacture.

As long as the properties of the implant materials are taken intoaccount any thread pitch, thread thickness and cutting edge are possibleup the point where the material is too thin to support the load placedon it. Threads and cutting edges that are too thin may break underhigher torques or distort during insertion.

Reduction of Insertion Torque

Experiments were performed comparing the insertion of the implant of thepresent invention with an equal diameter implant using classic cuttingflukes. In the test protocol, high density polyurethane was used tosimulate bone. A block of polyurethane was secured to a work station and3.2 mm holes drilled in the block. The implants were then inserted usinga digital torque wrench (Tohnichi, Japan). The insertion torque wasrecorded in Newton centimeters after each complete turn and the datarecorded. These data are shown in Tables 1 and 2 below.

TABLE 1 Insertion Torque for Improved Cutting Flukes Insertion torquefor implant having improved cutting flutes), 0.125 (3.2 mm) hole #ofSample Sample Sample Sample Sample turns 1 2 3 4 5 Average 1 6 6 6 6 6 210 10 9 6 8.75 3 12 12 12 9 11.25 4 13 14 15 10 13 5 15 16 17 12 15 6 1618 19 14 16.75 7 17 19 22 16 18.5 8 20 21 23 19 20.75 9 22 23 23 20 2210 26 26 26 22 25 11 27 28 29 23 26.75 12 31 28 31 29 29.75 13 42 45 4745 44.75

TABLE 2 Insertion Torque for Classic Cutting Flutes Insertion torque forimplant w/ classic cutting flutes 0.125 (3.2 mm) hole #of turns Test 1Test 2 Test 3 Test 4 Average 1 4 6 5 7 5.5 2 8 10 9 9 9 3 10 11 11 1010.5 4 12 13 14 13 13 5 16 18 15 16 16.25 6 18 19 19 19 18.75 7 22 22 2423 22.75 8 25 27 29 27 27 9 32 33 35 32 33 10 37 41 42 38 39.5 11 44 4951 47 47.75 12 54 62 65 59 60 13 67 78 80 77 75.5

The data in Tables 1 and 2 shows that the insertion torque of theimplant of the present invention is comparable to the insertion torqueof the classic design for shallower insertion depths. However, as depthof insertion increases, the classic implant design requiressignificantly more torque to insert in contrast to the implant of thepresent invention. These same data are graphed in FIGS. 6 and 7.

Referring to FIG. 8 which is a line graph comparing the average torquesrecorded for each turn in Tables 1 and 2 above. FIG. 8 shows that thecutting flukes of the present invention require substantially lesstorque as the implant is turned deeper into the socket. The presentinvention only required an average of 16.75 Ncm of torque duringinsertion of turn 8 compared with 27 Ncm of torque for the version ofthe implant having classic cutting flukes. The results are even moredramatic at 13 turns in which the present invention only required 44.75Ncm of torque compared to 75.5 Ncm of torque for the version of theimplant having classic cutting flukes. The present invention will alloweasier insertion by a surgeon and reduce the discomfort felt by thepatient.

A second set of experiments were performed to further test insertiontorque. Table 3 below shows the insertion torque for a conventionalimplant.

TABLE 3 Insertion Torque for Present Invention Implant Number/Torque (Ncm) Mean Std. Turns 1 2 3 4 5 6 7 8 9 10 11 12 Torque Dev 1 1 1.8 2.4 12.6 1 1 1.4 1.4 3.6 2.4 5.6 2.1 1.376 2 3.2 2 3.8 1.2 10.2 1.4 1.2 8 63.8 2.4 13.2 4.7 3.895 3 3.8 2.6 17.4 1.6 17.4 5.2 1.6 16.8 15.6 4.412.4 22.4 8.37 7.599 4 4.4 3.7 42.2 5.2 31.6 8.4 6.6 27.2 23.8 9.4 2128.2 17.6 12.97 5 5.8 5.6 48 6.4 35.4 11.6 13.4 39.6 37 19.4 36.4 44.425.25 16.34 6 6.8 15.8 64.8 7.2 41 18.2 20.4 55.4 49.4 25.2 47.8 56 3420.6 7 13.4 22.8 82.6 8 54.8 24.4 26.6 59.2 49.4 40 49.2 72 41.9 23.37 820.4 37.8 83.8 9.2 70.4 42.8 29.4 60 62.6 54 54.4 88 51.1 24.21 9 29.249.2 91.8 11.1 92.6 58.2 47.4 74.8 80.2 67.2 66.4 101.2 61.1 26.81 10 3563.8 113.2 12.6 101.2 64.6 58.4 94.2 98.2 79.8 84.8 126.2 77.67 32.63 1143.8 78.4 13.2 123.4 67.2 76.6 121.2 130.8 96.2 97.8 84.9 12 59.2 9015.8 84.2 76.6 122.6 136.2 83.5 height 3.71 3.77 3.71. 3.74 3.79 3.73.72 3.7 3.71 3.91 3.81 3.84 (mm)

TABLE 4 Insertion Torque for Fluted implants. Implant Number/Torque (Ncm) Mean Std. Turns 1 2 3 4 5 6 7 8 9 10 11 12 Torque Dev 1 10.8 9.2 7.68.6 9.2 8.4 9.2 9.4 7.4 6.2 6.6 7.2 8.317 1.34 2 13.6 18.8 13.6 15.214.8 19.2 18.6 16.8 15.8 12.8 18.2 17.6 16.25 2.26 3 22 27.6 18.2 18.626.8 27.8 30.6 28.6 24 23.2 28.8 24.4 25.05 4.02 4 28.2 45 26.6 26.629.4 40.4 45.6 42.4 34.8 38.6 41 40 36.55 7.14 5 41.8 58.4 43.4 40.244.4 54.6 54.2 58 45 49.8 47.4 54.2 49.28 6.43 6 59 71.4 57.2 50.6 60.270.8 73.2 74.6 60.2 61 59.4 69.8 63.95 7.64 7 85.2 78.2 78.4 70.4 84.294.2 93.8 92.2 81.8 81 80.2 93.8 84.45 7.63 8 106.4 94.2 105.4 98.8106.8 131.8 134.2 121.2 108.6 107.2 101 140.8 113 15.18 9 132.8 120.8129 123.8 135 170.2 168.2 151.2 124.6 139.6 125 152.2 139.4 17.24 10159.2 145.6 158.4 156 185.2 202.4 200.4 185.2 160.2 161.2 167.4 184172.1 18.59 height 3.62 3.56 3.6 3.71 3.72 3.72 3.66 3.6 3.66 3.86 3.833.88 (mm)

Table 5 below shows the insertion torque for a non-fluted implant.

TABLE 5 Insertion Torque for Non-Fluted Implant. Implant Number/Torque(N cm) Mean Turns 1 2 3 4 5 6 7 8 9 10 11 12 Torque STD 1 18.8 4.8 13.48.8 9.4 11.2 8.4 10.4 3.6 6.4 15.2 5.6 9.67 4.48 2 44.8 39.4 39 39.624.4 39 37.4 41.2 21.8 36.2 43.8 23.8 35.87 7.95 3 74.6 71.8 70.2 71.449.2 69.8 68.6 69.8 41.6 67.6 71 46.2 64.32 11.49 4 103.6 96.4 98.2 99.272.2 96.6 99 98.8 59 99.4 97.2 68.2 90.65 14.98 5 133 121.4 124 131.4101.2 126.4 125 130.4 78.6 128.4 123.2 89.2 117.7 17.90 6 159.6 142155.4 152.6 123.2 158.8 143.8 162.4 94.4 162.2 150.6 106.6 142.6 22.67 7182.8 159.8 177.2 186.4 139.2 176.6 173.4 190.6 114.8 200.2 176.8 125.6167 26.77 8 198 199 199.8 207.6 151.4 203 198.4 200.2 126.6 213.6 204141.8 187 29.18 9 213.8 208.6 222.8 209.8 166.6 221.8 212 221.6 157.8232.6 218.6 176.8 205.2 24.27 height 4.41 4.47 4.41 4.42 4.34 4.44 4.434.48 4.42 4.48 4.49 4.5 (mm)

Referring now to FIG. 9 which is a line graph comparing the averageinsertion torques over 8 turns for implants of the present invention,fluted implants and non-fluted implants. As can be readily seen, theimplants of the present design require substantially less torque forinsertion. This results in less discomfort to the patient, less effortfor the dentist and as show below a more stable implant.

Reduction of Micromotion

Most implants require from 3-6 months to stabilize followingimplantation before a prosthesis can be installed. This is because theimplants are subject to small amounts of motion called micromotion,movement between the bone and the implant, in the range of a few micronsto almost a millimeter in bad cases. This is believed to be caused by anumber of factors. In many cases, when a hole is drilled, the bore maynot be uniformly round and may have voids or protruding portionssurround the hole. When an implant is inserted into the bore, it willfollow the path of least resistance and will be pushed aside in regionswhere there is a protrusion in the wall and will follow areas wherethere is a void in the wall. Conventional implants press upon the wallsof the bore more than they cut a thread. The course nature of cuttinggrooves on conventional implants require sufficiently high torque thatthey will be pushed aside rather than cut a thread as it follows thepath of least resistance. If the implant is not true in the bore, itwill have greater motion until bone grows around it and before it can besafely loaded by chewing. Typically, this waiting period is 3-6 months.

Additionally, the areas of bone which are subject to pressure from theimplant will initially experience absorption of the bone before new boneis deposited. This results in a loosening of the initial fit of theimplant.

Implantation of conventional self-tapping implants is usually spreadover 3-6 months. On the initial visit, the bore for the implant will bedrilled and the implants placed. The patient must then wait until newbone growth stabilizes the implants at which point the patient returnsfor installation of any prosthesis. The total chair time for a patientimplanted with conventional implants can be between 20-30 hours forimplantation of 24 implants with prosthetic teeth. The cost for such aprocedure can exceed one hundred thousand dollars and requires multiplevisits to the dentist.

Applicant was surprised to learn that the implants of the present designsubstantially eliminate micromotion and therefore allow immediateloading of the implant. Without being limited to any theory, thereduction of micromotion is believed to result from a combination offactors. First, the sharp cutting surfaces are believed to overcome theforces exerted by protrusions in the bore allowing the implant to beinserted true to the bore. Second, because the implant cuts bettergrooves, there are fewer regions of high pressure and therefore lessbone absorption following implantation.

Patients undergoing treatment with the implant of the present inventioncan be treated in as few as four to five hours of time in the dentalchair. The bores are drilled, the implants inserted and if available,the prosthesis can be attached on the same day if it is available.Potentially, the reduction in time spent in the chair reduces patientcosts to about twenty five percent of the cost of conventional implants.

Implant Micromotion Determined by Applied Force

A total of 36 titanium implants representing three categories: animplant of the present invention, a fluted conventional implant and anon-fluted conventional implant, were loaded onto six, 5 cm×5 cm solid,rigid polyurethane foam blocks (Sawbones, Wash., USA) simulating bonewith a hardness of D2. Each implant was fitted with a one-piece abutmentto allow for the application of a load. Identical abutments were usedthroughout the procedure. A groove has been machined on each abutment,in order to make sure that the point of application of the force to thecrest of the bone is always the same. A customized loading device,consisting of a digital micrometer (Mitutoyo Absolute Digimatic) anddigital force gauge (Chantillion E-DFE-025) was used to determineimplant micromotion.

The implants were placed in the polyurethane foam blocks utilizing theTohnichi Digital Torque Gauge. The implants were loaded into thepolyurethane block up to the base of the micro-thread. Torque has beenrecorded after each turn of the implant into the blocks. The abutmentwas then placed on the implant and secured using an insertion torque of35 N cm as measured by a TOHNICHI Digital Torque Gauge Model BTGE IOCN.

After the implants were placed, the polyurethane blocks were fixed on acustomized loading apparatus for the evaluation of micromovement. Theapparatus consisted of a digital force gauge [Chantillion E-DFE-025]vertically fixed onto a frame and, on the opposite side, a digitalmicrometer [Mitutoyo Absolute Digimatic] that measured the micromotionof the abutment during the load application. The forces were achieved byturning a dial, which controlled the height of the force gauge. Thisdialed-in force was applied to the abutment via a lever. The micrometerwas placed tangent to the crown of the abutment to detect displacement.Loads were tested on each implant starting at 10 N cm and continuing to100 N cm and measured at 5 N cm increments.

Table 6 below shows the micromovement of an implant of the presentinvention.

TABLE 6 Micromovement of Implant of Present Invention Mean Force ImplantNumber/Motion Disp.t Std ((N) 1 2 3 4 5 6 7 8 9 10 11 12 (mm) Dev 100.027 0.031 0.029 0.015 0.024 0.033 0.027 0.03 0.025 0.034 0.032 0.030.03 0.01 15 0.053 0.05 0.043 0.031 0.038 0.059 0.048 0.063 0.049 0.0590.05 0.043 0.05 0.01 20 0.07 0.068 0.058 0.051 0.057 0.084 0.068 0.1020.088 0.1 0.066 0.059 0.07 0.02 25 0.095 0.091 0.081 0.066 0.076 0.1140.096 0.115 0.112 0.135 0.088 0.082 0.10 0.02 30 0.116 0.113 0.102 0.0890.098 0.136 0.121 0.136 0.133 0.162 0.106 0.107 0.12 0.02 35 0.14 0.1330.125 0.108 0.124 0.166 0.15 0.155 0.153 0.19 0.133 0.126 0.14 0.02 400.164 0.156 0.15 0.129 0.148 0.193 0.175 0.179 0.172 0.21 0.158 0.1490.17 0.02 45 0.187 0.184 0.173 0.15 0.173 0.223 0.206 0.201 0.193 0.2360.187 0.171 0.19 0.02 50 0.214 0.207 0.2 0.175 0.201 0.252 0.237 0.2260.217 0.265 0.218 0.197 0.22 0.02 55 0.238 0.234 0.224 0.202 0.23 0.2840.28 0.257 0.237 0.287 0.249 0.22 0.25 0.03 60 0.263 0.264 0.251 0.2310.259 0.316 0.305 0.279 0.26 0.315 0.283 0.238 0.27 0.03 65 0.291 0.2910.279 0.259 0.294 0.351 0.34 0.308 0.285 0.346 0.323 0.27 0.30 0.03 700.324 0.32 0.307 0.287 0.324 0.386 0.374 0.339 0.309 0.378 0.364 0.2970.33 0.03 75 0.346 0.348 0.335 0.315 0.358 0.42 0.409 0.377 0.335 0.4120.4 0.324 0.36 0.04 80 0.376 0.376 0.364 0.343 0.39 0.454 0.449 0.390.361 0.448 0.438 0.355 0.40 0.04 85 0.408 0.411 0.39 0.375 0.426 0.4920.486 0.42 0.385 0.478 0.483 0.383 0.43 0.04 90 0.437 0.439 0.42 0.4050.459 0.532 0.523 0.447 0.413 0.516 0.518 0.412 0.46 0.049 95 0.4680.472 0.452 0.445 0.498 0.597 0.561 0.48 0.44 0.552 0.575 0.443 0.460.057 100 0.5 0.505 0.477 0.477 0.53 0.616 0.598 0.511 0.469 0.587 0.6150.475 0.53 0.058

Table 7 below shows the micromovement of a conventional fluted implant.The mean displacement is higher than in the implants of the presentinvention.

TABLE 7 Micromovement of a Conventional Fluted Implant Mean ForceImplant Number/Motion mm Displ Std ((N) 1 2 3 4 5 6 7 8 9 10 11 12 (mm)Dev 10 0.025 0.029 0.02 0.026 0.023 0.029 0.02 0.018 0.019 0.029 0.0360.026 0.03 0.01 15 0.038 0.045 0.052 0.041 0.034 0.103 0.072 0.048 0.0450.044 0.09 0.05 0.06 0.02 20 0.053 0.065 0.111 0.056 0.048 0.174 0.130.113 0.081 0.061 0.148 0.082 0.09 0.04 25 0.072 0.097 0.142 0.077 0.0880.242 0.207 0.197 0.128 0.121 0.181 0.139 0.14 0.06 30 0.09 0.17 0.1640.123 0.131 0.277 0.274 0.24 0.203 0.206 0.215 0.179 0.19 0.06 35 0.110.26 0.188 0.188 0.177 0.318 0.306 0.27 0.24 0.234 0.249 0.204 0.23 0.0640 0.131 0.339 0.207 0.238 0.219 0.345 0.319 0.291 0.262 0.26 0.2810.227 0.26 0.06 45 0.15 0.37 0.227 0.266 0.239 0.372 0.338 0.312 0.2860.287 0.315 0.253 0.28 0.06 50 0.172 0.395 0.248 0.293 0.26 0.403 0.3560.331 0.312 0.313 0.351 0.276 0.31 0.07 55 0.194 0.422 0.269 0.347 0.2830.441 0.38 0.351 0.341 0.34 0.371 0.308 0.34 0.07 60 0.216 0.452 0.2940.362 0.303 0.463 0.401 0.372 0.367 0.37 0.402 0.33 0.36 0.07 65 0.2410.473 0.316 0.379 0.324 0.492 0.425 0.39 0.386 0.399 0.443 0.354 0.390.07 70 0.264 0.5 0.34 0.406 0.353 0.525 0.448 0.412 0.415 0.425 0.4650.38 0.41 0.07 75 0.288 0.534 0.365 0.435 0.374 0.554 0.474 0.44 0.4460.453 0.495 0.402 0.44 0.07 80 0.312 0.559 0.391 0.468 0.395 0.585 0.4980.47 0.473 0.482 0.528 0.429 0.47 0.08 85 0.337 0.601 0.418 0.498 0.4210.618 0.524 0.501 0.5 0.51 0.567 0.456 0.50 0.08 90 0.382 0.628 0.4470.525 0.441 0.648 0.551 0.528 0.526 0.539 0.594 0.484 0.52 0.08 95 0.4080.66 0.48 0.563 0.466 0.679 0.574 0.561 0.559 0.571 0.627 0.513 0.560.08 100 0.427 0.694 0.511 0.599 0.494 0.705 0.6 0.592 0.588 0.602 0.6720.547 0.59 0.08

Table 8 shows the micromovement of a conventional non-fluted implant.The mean displacement is higher still than either the present inventionor the conventional fluted implant.

TABLE 8 Micromovement of a Conventional Non-fluted Implant. Mean ForceImplant Number/Motion mm Disp. Std ((N) 1 2 3 4 5 6 7 8 9 10 11 12 (mm)Dev 10 0.032 0.032 0.023 0.056 0.026 0.104 0.028 0.067 0.011 0.014 0.0910.028 0.04 0.03 15 0.059 0.067 0.048 0.074 0.045 0.198 0.077 0.116 0.0270.049 0.177 0.054 0.08 0.05 20 0.094 0.114 0.077 0.116 0.08 0.31 0.1450.171 0.088 0.102 0.255 0.096 0.14 0.07 25 0.132 0.185 0.099 0.175 0.120.433 0.188 0.242 0.125 0.168 0.343 0.132 0.20 0.10 30 0.163 0.231 0.1230.226 0.168 0.534 0.218 0.32 0.183 0.229 0.432 0.18 0.25 0.12 35 0.2210.259 0.143 0.258 0.235 0.649 0.248 0.403 0.244 0.331 0.538 0.228 0.310.15 40 0.258 0.284 0.164 0.289 0.283 0.74 0.28 0.456 0.297 0.428 0.620.264 0.36 0.17 45 0.292 0.31 0.185 0.317 0.307 0.796 0.304 0.501 0.3290.505 0.703 0.287 0.40 0.19 50 0.322 0.335 0.207 0.343 0.331 0.862 0.3310.541 0.35 0.573 0.798 0.317 0.44 0.21 55 0.351 0.358 0.227 0.373 0.3560.915 0.358 0.579 0.375 0.615 0.86 0.346 0.48 0.22 60 0.379 0.383 0.2480.399 0.381 0.945 0.388 0.615 0.4 0.65 0.896 0.373 0.50 0.22 65 0.4050.407 0.273 0.427 0.404 0.98 0.417 0.649 0.425 0.707 0.933 0.403 0.540.23 70 0.432 0.434 0.293 0.456 0.432 1.019 0.445 0.684 0.45 0.764 0.9660.431 0.57 0.23 75 0.465 0.46 0.318 0.489 0.457 1.054 0.474 0.723 0.4790.804 0.995 0.461 0.60 0.24 80 0.491 0.49 0.336 0.52 0.485 1.091 0.5090.763 0.505 0.845 1.03 0.496 0.63 0.24 85 0.524 0.521 0.36 0.535 0.5131.143 0.545 0.8 0.542 0.888 1.08 0.569 0.67 0.25 90 0.558 0.553 0.3850.552 0.545 1.191 0.583 0.839 0.57 0.959 1.113 0.569 0.70 0.26 95 0.5880.59 0.41 0.605 0.58 1.238 0.631 0.881 0.596 1.024 1.163 0.607 0.74 0.27100 0.632 0.623 0.435 0.642 0.616 1 0.67 0.924 0.639 1.074 1.197 0.6490.78 0.27

FIG. 10 is a line graph of the mean displacement data from tables 7, 8and 9. The reduction of micromotion is readily apparent in FIG. 10.

In yet another embodiment devices of the present invention, implants ofthe present invention can be used to support osseointegrated hearingaids. Osseointegrated hearing aids are those in which the sound ismechanically transmitted through bone. These aids include an implantwhich is inserted into the skull. A hearing aid transducer is affixed tothe implant. Referring to FIGS. 1-3, an implant for a hearing aid can beconstructed in the same manner as a dental implant taking into accountthe thickness of the skull where it will be implanted. The implantcomprises a substantially cylindrical body 1 having a proximal end 2 anda distal end 3. The proximal end contains a prosthetic platform 7 ontowhich a the hearing aid 100 will be fitted. The body contains at leastone external helical thread 9 which runs from the distal end 3 to theproximal end 2. The helical thread 9 may be right or left handed andcontains at least one cutting edge 6 for each turn of the cutting head.The implant further comprises a second helix 10 running in the oppositedirection of the helical thread from the distal end 3 to the proximalend 2. The second helix can be seen more clearly in FIG. 4 in which thehelical thread 9 has been omitted for clarity. The hearing aid on theimplant can be seen in FIG. 11.

Because the implant of the present invention requires a smaller pilothole than conventional implants, the implant is more secure and willenable a hearing aid in many instances to be mounted immediately.

The implant of the present invention is used in a conventional manner.The surgeon will drill a pilot hole for the implant. The implant isattached to an insertion tool and turned into the pilot hole. Uponturning, the cutting edge 6 will cut a groove into the bone into whichthe helical thread 9 will follow. Because cutting edge 6 has a sharpedge leading into a narrow plateau on the helical thread 9, less bonedebris is generated. This debris is pushed towards the proximal end ofthe body through the second helical groove 10. This movement of debriskeeps the pilot hole relatively free from debris thereby preventingdebris from filling the pilot hole or binding or jamming the implant.This reduces incidences of the implant prematurely bottoming out in thepilot hole because of debris filling the hole and reduces the debriscaught in the helical groove thereby reducing friction on the cuttingsurfaces which reduces the torque required for insertion.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms disclosed but, on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and cope of the invention as defined by theappended claims.

What is claimed is:
 1. A method for installing a self-threading implantin bone, the method including the steps of: engaging a distal end of animplant against a bone; driving the implant into the bone by rotatingthe implant around a rotational axis of the implant and thus drivinginto the bone; a helical thread coaxially wound around at least aportion of a body of the implant, and a first blade formed in the threadand having an arcuate cutting edge that curves helically aft andradially outward from adjacent a minor thread diameter to merge with athread ridge at a major thread diameter; generating bone debris as theimplant is driven into the bone; distributing the generated bone debrisacross a body length of the implant by moving the generated bone debrisin a direction, relative to the implant, that is rotationally in thedirection of implant rotation and axially outward toward a proximal endof the implant, as the implant is driven into the bone.
 2. The method ofclaim 1 in which the distributing step includes moving the generatedbone debris outward and in the direction of implant rotation via ahelical groove formed coaxially into the thread and having a handednessopposite that of the thread.
 3. The method of claim 1 in which the stepof driving the implant into bone includes passing into the bone a secondblade formed in the thread and having an arcuate cutting edge thatcurves helically aft and radially outward from adjacent a minor threaddiameter to merge with a thread ridge at a major thread diameter, aforward surface of the first blade being in helical alignment with aforward surface of the second blade, the helical alignment of theforward blade surfaces being in opposite handedness to the helicalthread.
 4. The method of claim 1 in which the step of moving the bonedebris outward includes receiving the bone debris in a helical grooveformed coaxially into the thread and having a handedness opposite thatof the thread.